1. Field of the Invention
This invention relates to a bicycle wheel rim, more particularly to a bicycle wheel rim which is provided with a weld connection and which has two opposite brake pad contacting surfaces that are free of any weld flash.
2. Description of the Related Art
A conventional bicycle wheel rim is generally produced by forming a metal strip, such as from extruded aluminum, cutting and bending the metal strip to form an annular shape with a predetermined size, and bonding two opposite end portions of the metal strip by flash-welding to form an annular frame. When electric current flows through the opposite end portions of the metal strip during the flash-welding process, a layer of molten metal is formed between the end portions of the metal strip to bond together the same. However, since weld flash produced during the flash-welding process would unavoidably extend to two brake pad contacting surfaces of the annular frame, the brake pad contacting surfaces must be polished after the flash-welding process. Moreover, the end portions of the metal strip become brittle after the flash-welding process.
To solve the aforementioned drawbacks, it has been proposed heretofore to provide a connecting member for interconnecting the end portions of the metal strip. Referring to FIGS. 1 and 2, a conventional bicycle wheel rim 1 is shown to include an annular frame 11 and a connecting member 10. The annular frame 11 is formed from an aluminum metal strip with two opposite end portions, and includes two spaced annular tire retaining walls 12 which have inner edges proximate to a central axis of the annular frame 11 and two opposite brake pad contacting surfaces 121, an annular inner spoke mounting wall 13 interconnecting the inner edges of the tire retaining walls 12, and an annular outer connecting wall 14 disposed around the spoke mounting wall 13 and interconnecting the tire retaining walls 12. The tire retaining walls 12, the inner spoke mounting wall 13 and the outer connecting wall 14 cooperatively confine an annular channel 15. The connecting member 10 has a cross-section corresponding to that of the annular channel 15. After applying an adhesive on the outer surface of the connecting member 10, the connecting member 10 is fitted in the annular channel 15 so as to extend into the end portions of the annular frame 11 for bonding together the end portions of the annular frame 11.
With the use of the connecting member 10 to adhesively connect the end portions of the metal strip for bonding together the end portions, a flash-welding process and a succeeding polishing step can be obviated. However, when the bicycle wheel rim is subjected to an electroplating process after assembly thereof, the adhesive is likely to degrade and generate an undesired gas under the high temperature environment of the electroplating process, thereby adversely affecting the strength of the connection between the end portions of the metal strip.
Referring again to FIGS. 1 and 2, the bicycle wheel rim 1 is mounted on a bicycle hub 19 by means of a plurality of spokes 17. To mount the spokes 17 on the bicycle wheel rim 1, the inner spoke mounting wall 13 is formed with a plurality of inner spoke mounting holes 131, while the outer connecting wall 14 is formed with a plurality of outer spoke mounting holes 141 that are registered with the inner spoke mounting holes 131, respectively. Each of the outer spoke mounting holes 141 permits extension of a spoke fastener 18 of a respective one of the spokes 17 therethrough, and is larger than the corresponding inner spoke mounting hole 131 so that the spoke fastener 18 abuts against a rim portion of the corresponding inner spoke mounting hole 131. In design, it is desirable to make the connecting member 10 longer, usually longer than the distance between adjacent pairs of the inner spoke mounting holes 131 (or the outer spoke mounting holes 141) to increase the bonding strength between the end portions of the metal strip. As such, the connecting member 10 should be formed with through holes that are aligned with the corresponding inner and outer spoke mounting holes 131, 141 to permit extension of at least one spoke 17' therethrough. As shown in FIG. 3, when the spoke 17' extends through the connecting member 10, the spoke fastener 18' of the spoke 17' abuts against an inner wall surface of the connecting member 10, rather than the spoke mounting wall 13. Therefore, the tension of the spoke 17' that extends through the connecting member 10 differs from that of the other spokes 17 (see FIG. 2) which do not extend through the connecting member 10. Thus, when the wheel rim 11 is subjected to impact, the end portions of the metal strip are still liable to release from one another even if the connecting member 10 has been made longer.